A review from Amazon.com:
The lovable mystery writer, Mrs. Ariadne Oliver, is visiting a friend in a London suburb called Woodleigh Common and helping host a party for the community's teenagers. There are costumes, pumpkins, games, and...oh, yes...a murder, of course. The young girl who earlier in the evening had bragged that she had once witnessed a murder is found dead in the tub used to bob for apples. Mrs. Oliver hurries to London to locate her friend Hercule Poirot and ask for his assistance. Poirot would not think of turning down his old friend and immediately sets about learning all he can regarding the residents of Woodleigh Common. An au pair girl who has mysteriously vanished and a landscape architect who loves his work are just two of the interesting characters Poirot will deal with before his little grey cells put the pieces of the puzzle together in time to prevent another murder.